[Eeglablist] ICA runs slowly and returns complex numbers

[Ilana Podlipsky]

Dear Arno,

Thank you for your input.
Can you elaborate why ICA on bipolar montage is not good? Can you give me a
reference for this?
>From our experience it works quite well and separates well into reasonable
components of signal and artifact.

Thank you
Ilana


On Tue, Nov 26, 2013 at 8:23 AM, Arnaud Delorme <arno at ucsd.edu> wrote:

> Dear Llana,
>
> if ICA detects a rank of 57, then this is probably what you should use.
> ICA on bipolar montage will not be informative. ICA will attempt to model
> each channel reference so that common sources may be projected to all
> channels in a linear fashion.
> Best,
>
> Arno
>
> On Nov 24, 2013, at 3:18 AM, Ilana Podlipsky <ilana.mlist at gmail.com>
> wrote:
>
> Dear Arno,
>
> Judging by the ICA output in Matlab the solution converges but very very
> slowly.
> I use bipolar montage, each electrode is referenced to its neighbor. I use
> 64 electrodes recorded with one reference electrode and convert  it to 85
> differential channels off line. ICA detects rank 57 but I changed it
> manually to 64 since this is the original number of channels, is that
> correct?
> Meanwhile I tried binica on the same computer running Ubuntu, and it runs
> much faster (in 20 minutes). I would still like to resolve this issue
> because I'd prefer to work on Windows.
>
> Thanks,
> Ilana
>
>
>
> On Wed, Nov 20, 2013 at 6:59 PM, Arnaud Delorme <arno at ucsd.edu> wrote:
>
>> Dear Ilana,
>>
>> did your ICA solution converge (meaning that the weight difference
>> decrease with time). This might be the issue.
>> Also, are you using average reference or linked mastoid. In this case,
>> the data matrix rank is the number of channels minus 1. ICA tries to detect
>> this automatically but sometimes fails. You then have to manually reduce
>> the number of dimension by 1 when running ICA. If you have 64 channels, in
>> the edit box for running ICA (where there is already 'extended', 1) you may
>> add 'pca', 63.
>>
>> Best,
>>
>> Arno
>>
>> On Nov 12, 2013, at 11:54 PM, Ilana Podlipsky <ilana.mlist at gmail.com>
>> wrote:
>>
>> > Hi All,
>> >
>> > Since I've recently changed my computer ICA in eeglab runs very very
>> slowly and returns complex numbers.
>> > On my previous computer, on the same data I ran the same ICA  within an
>> hour or two. On the new computer the same ICA takes more than 24 hours,
>> After 512 steps it returns this message :
>> >
>> > Sorting components in descending order of mean projected variance ...
>> > Warning: Matrix is close to singular or badly scaled.
>> >          Results may be inaccurate. RCOND = 6.956943e-019.
>> >
>> > When I try to plot the ICA activations I don't see any traces and when
>> I look into the EEG.icaact matrix I see only complex numbers. Tried both
>> runica and binica.
>> > This has never happen to me with the old computer on the same dataset.
>> > Both the old and new computer run Win7 64bit, matlab 2008a and eeglab
>> 12. The hardware of the computers is different.
>> >
>> > What could be the reason for this, and what can ?I do to solve this?
>> >
>> > Thanks for the help,
>> > Ilana
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>
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